The present invention relates to a stacking device, and more particularly, to a stacking device for stacking sheet material. The present invention is particularly applicable in stacking cut-to-length sheets from a generally continuous source, and shall be described with particular reference thereto. It will, of course, be appreciated that the present invention has other broader applications and may be used in stacking other types of sheet material.
Many types of sheet material are produced by a process wherein individual sheets are cut from a generally continuous strip or web of material. It is then necessary to stack these xe2x80x9ccut-to-length sheetsxe2x80x9d for packaging and/or shipping. In the process of stacking and/or shipping these xe2x80x9ccut-to-length sheetsxe2x80x9d, it is often desirable to minimize the contact between the sheets and the stacking device so as not to damage the sheets.
The present invention provides a device for stacking sheet material, such as cut-to-length sheets that are cut from a generally continuous source, that minimizes physical handling and gripping of the sheet.
In accordance with the present invention, there is provided a sheet stacking device, comprised of a sheet support bed comprised of a plurality of side-by-side rollers. Each of the rollers is freely rotatable about a respective roller axis. A support bed drive assembly is provided for moving the sheet support bed in a predetermined direction along a closed path. The path has an upper horizontal run and a lower horizontal ran and is dimensioned such that a gap exists between a leading end and a trailing end of the sheet support bed. The gap moves along the path as the sheet support bed moves along the path. A roller control assembly is provided for selectively controlling rotation of each of the rollers about its respective roller axis. A controller selectively and sequentially controls the operation of the support bed drive assembly and the roller drive assembly. The stacking device is operable to perform the following operational steps:
a) causing the support bed drive assembly to move the sheet support bed to a sheet receiving position on the upper run of the path;
b) causing the roller control assembly to allow the rollers to rotate freely to receive a sheet to be stacked on the support bed;
c) causing the support bed drive assembly to move the sheet support bed at a predetermined speed along the path to move the sheet to a xe2x80x9cstacking positionxe2x80x9d;
d) when the sheet is at the stacking position, causing the roller control assembly to rotate the roller in a predetermined direction at a predetermined speed while the support bed continues to move along the path, wherein the rollers are operable to convey the sheet in a direction opposite the direction of the support bed at a speed wherein the sheet remains essentially stationary at the xe2x80x9cstacking positionxe2x80x9d;
e) continuously driving the sheet support bed along the path and continuously rotating the roller wherein the sheet becomes unsupported as the trailing end of the sheet support bed passes under the sheet and the sheet drops through the gap onto the sheet support bed as it moves along the lower run;
f) causing the rollers along the lower run to rotate at a predetermined speed in a predetermined direction wherein the sheet is conveyed in a direction opposite the direction of the support bed at a speed wherein the sheet remains essentially stationary at a position essentially below the stacking position; and
g) continuously driving the sheet support bed along the path and continuously rotating the roller along the lower run wherein the sheet becomes unsupported as the trailing end of the sheet support bed passes under the sheet and the sheet drops through the gap onto a stacking platform.
In accordance with another aspect of the present invention, there is provided a sheet stacking device, comprised of a sheet support bed having a first end and a second end. The sheet support bed is comprised of a plurality of side-by-side rollers, each of the rollers being freely rotatable about an associated roller axis. A drive assembly moves the sheet support bed in a predetermined direction along a closed path, the path having a horizontal upper run and a horizontal lower run, and is dimensioned such that a space exists between the first end and the second end of the sheet support bed as the sheet support bed moves along the path. A roller control assembly selectively and sequentially controls rotation of select ones of the rollers at select intervals during a stacking operation, wherein the stacking device is operable to:
receive a sheet to be stacked on the sheet support bed when the support bed is disposed along the upper run;
convey the sheet along the upper run on the support bed to a xe2x80x9cstaking positionxe2x80x9d on the upper run;
cause the roller control assembly to rotate rollers disposed along the upper run in a direction such that the sheet remains essentially in the stacking position as the sheet support bed continues to move along the path, the sheet dropping through the space between the first and the second end of the sheet support bed onto the rollers of the sheet support bed on the lower run when the support bed moves from the upper run to the lower run; and
cause the roller control assembly to rotate rollers disposed along the lower run in a direction such that the sheet remains essentially in the stacking position as the sheet support bed continues to move along the path, the sheet dropping through the space between the first end and the second end of the sheet support bed onto a stack of sheets when the support bed moves from the lower run to the upper run.
In accordance with another aspect of the present invention, there is provided a method of stacking sheet material, comprising the steps of:
a) conveying a sheet to be stacked onto the surface of a sheet support bed, the support bed comprised of a plurality of side-by-side rollers, each of the rollers being rotatable about a respective roller axis, the support bed being movable in a predetermined direction along a closed path having a horizontal upper run and a horizontal lower run, the path dimensioned such that a space exists between distal ends of the support bed, the space moving along the path as the support bed moves along the path;
b) moving the support bed along the path to move the sheet along the upper path run toward a stacking position;
c) causing the rollers along the upper run to rotate when the sheet reaches the stacking position, the roller rotating in a direction such that the sheet remains essentially stationary on the support bed at the stacking position as the support bed continues to move along the path, the sheet falling generally vertically onto the support bed on the lower run when the space moves under the sheet;
d) causing the rollers along the lower run to rotate in a direction such that the sheet falling on the support bed from the upper run remains essentially stationary on the support as the support bed continues to move along the path, the sheet falling from the lower run of the support bed when the space moves under the sheet; and
e) collecting the sheet at a stacking location below the lower run.
It is an object of the present invention to provide a stacking device for stacking sheet material.
It is another object of the present invention to provide a stacking device for stacking xe2x80x9ccut-to-length sheetsxe2x80x9d from a generally continuous source of sheet material.
It is another object of the present invention to provide a device as described above having means for detecting defects on a cut-to-length sheet.
It is a still further object of the present invention to provide a stacking device as described above that diverts cut-to-length sheets with defects from the stacking operation.
It is a still further object of the present invention to provide a stacking device that minimizes contact with the sheet material to be stacked.
These and other objects and advantages will become apparent from the following description of a preferred embodiments of the invention taken together with the accompanying drawings.